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Stock-Based Compensation - Stock option activity (Details) - $ / shares
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]      
Beginning balance (in shares) 6,589 34,123 143,224
Issued (in shares) 2,500 0 0
Exercised (in shares) (3,300) (26,784) (108,201)
Forfeited (in shares) 0 (750) (900)
Ending balance (in shares) 5,789 6,589 34,123
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]      
Beginning balance (in dollars per share) $ 19.99 $ 14.69 $ 9.13
Issued (in dollars per share) 47.95 0 0
Exercised (in dollars per share) 11.40 12.42 7.17
Forfeited (in dollars per share) 0 49.08 34
Ending balance (in dollars per share) $ 36.96 $ 19.99 $ 14.69